The invention relates to a method for controlling the operation of an internal combustion engine within a predetermined operational domain.
Due to the increasingly rigorous regulations concerning exhaust gas composition and in view of the general fuel shortage, there is a need for methods and means for operating internal combustion engines in a domain wherein the toxic components of the exhaust gas can be reduced to a minimum and/or in which a minimum amount of fuel is used.
The most obvious solution to meet such requirements is to operate the internal combustion engine with as lean a fuel-air mixture as possible, i.e., to operate the engine along the so-called lean running limit of the engine. In this operational domain, one may assume that the exhaust gas is relatively free from toxic components and that the fuel consumption will be relatively low. One of the possible parameters which characterizes the lean running limit appears to be the pressure in the cylinders of an internal combustion engine. When using this solution, the fuel-air mixture which is delivered to the internal combustion engine can be influenced by either enriching it with fuel or by making it leaner in dependence on the pressures as measured in the cylinders.
However, when this problem is considered more carefully, it is found that the pressure in the cylinders of the internal combustion engine is subject to considerable fluctuations which derive partly from uncontrollable operational conditions of the internal combustion engine, for example fluctuations of the air number of the charge and turbulence. When the pressure in the combustion chamber is determined from measurements of the angular speed of the crankshaft, there are additional error-producing influences, caused, for example, by the oscillating masses of the drive means for the crankshaft, an unevenness of the road on which the vehicle travels or by some other forces acting on the engine block of the internal combustion engine.
These fluctuations are superimposed on the normal pressure curve in a cylinder of the internal combustion engine and they result in fluctuations of the angular velocity of the crankshaft. These superimposed oscillations might be removed by the use of low-pass filters, but the use of such filters invites considerable problems because the internal combustion engine is to be operated in a wide rpm domain and it is very difficult to find filters which are equally suitable at both low and high rpm's (frequencies).